In order to measure a dimension of contact holes between wiring layers or gate electrodes in manufacturing a semiconductor device, an inspecting apparatus using a primary electron beam such as a critical-dimension scanning electron microscope (hereinafter, referred to as a CD-SEM) has been used as one type of charged particle beam application apparatuses.
Herein, FIG. 14 schematically shows an electron optical system of an SEM semiconductor inspecting apparatus used in the related art.
A primary electron beam 22 (shown by a dotted line) from an electron gun 1 by a voltage from an extraction electrode 2 is converged and deflected by passing through a condenser lens 3, a scanning deflector 5, an aperture 6, an objective lens 9, or the like, and is then irradiated at an inspecting position of a sample 10, i.e., a semiconductor device, etc. In addition, the condenser lens 3, the scanning deflector 5, the aperture 6, the objective lens 9, and a shield electrode 16 are formed in an axial symmetry shape based on an optical axis 18 as a central axis.
The sample 10 is applied with a deceleration voltage (hereinafter, referred to as a retarding voltage) from a retarding power supply 26 for decelerating the primary electron beam 22. A secondary electron beam 24 (shown by a dotted line) is generated from the sample 10 by irradiating the primary electron beam 22 and is accelerated by the retarding voltage applied to the sample 10 to be moved upward. The accelerated secondary electron beam 24 is deflected by an E cross B deflector 8 and is then input to a secondary electron detector 14. The secondary electron detector 14 converts the input secondary electron beam 24 into an electric signal, which is in turn amplified by a pre-amp (not shown) to a luminance modulating input for an inspection image signal, thereby obtaining an image data of an inspection region.
In manufacturing the semiconductor device, the sample 10 is a semiconductor wafer and plural rectangular chips are formed almost over the whole region of the sample 10. For this reason, the inspecting apparatus may perform the inspection on the chip at the central portion of the sample 10 as well as the chip formed at the peripheral portion. In the case of inspecting portions (for example, central portion) other than the outer peripheral portion of the sample 10, a equipotential surface of the vicinity of the sample 10 has an axial symmetry distribution using the optical axis 18 as the central axis, but in the case of inspecting the outer peripheral portion of the sample 10, there is a problem in that the axial symmetry of the equipotential surface 20 (shown by a dotted line) of the vicinity of the sample 10 is disordered as shown in FIG. 15. When the axial symmetry of the equipotential surface 20 is disordered, there is a problem in that the case in which the primary electron beam 22 is bent and the primary electron beam 22 arrives at a position 30 spaced apart from a position (a position where the optical axis 18 and the surface of the sample 10 intersects with each other) to be originally inspected on the sample 10, that is, a so-called, a position deviation occurs.
In the CD-SEM, the positions to be measured are detected by performing an approximate position adjustment using a mechanical stage and then, a high-precision position adjustment using the SEM phase. However, when the position deviation is large, the movement amount to the positions to be measured is increased since the position adjusted by using the mechanical stage and the position adjusted by using the SEM phase are far away from each other, thereby causing the degradation in throughput.
The diameter of the semiconductor wafer that is sample is increased, like a diameter of 300 mm or 450 mm. When the diameter of the semiconductor wafer is increased, the curvature in the outer edge thereof is small, such that it is possible to form rectangular device chips formed on the wafer to be further approximate to the outer edge of the semiconductor wafer than before. Accordingly, there is a need to inspect the outer edge as maximally as possible, than before, in manufacturing the semiconductor device. It is known that the above-mentioned position deviation amount is increased as the position to be inspected is at the outer edge of the semiconductor wafer. The problem of the position deviation that causes the bending of the primary electron beam is considered as a more important matter.
As a technology for preventing the disorder of the axial symmetry of the equipotential surface 20 at the outer peripheral portion of the sample, a technology of installing a conductive ring between an edge of the sample (herein, a substrate) and a substrate holder formed at the same height as the surface of the substrate that is the sample and applying voltage to the conductive ring is disclosed in Patent Document 1. Further, the technology controls the voltage applied to the conductive ring according to the gap size between the substrate edge and the substrate holder. It is possible to prevent the potential distribution from being disordered near the substrate by adopting the technology.
Prior Art Documents
Patent Document
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2004-235149